What happens to your muscles when you sit? 9 Oct 2020
Chair sitting is unique in that Gluteus maximi are totally relaxed at the same time as having an upright torso, and they are therefore not able to contribute to lumbar extension and back stabilization as they usually do. Without the help of the Gluteal muscles, the Erector Spinae muscles above become tired and painful in a very short time, and give up fighting to maintain the correct "hollow" in the lumbar spine.
The diagram on the left indicates what happens to three key muscles when you spend long periods of time sitting.
The Hamstrings (H) are shortened by sitting. Also, during sitting, the Gluteus Maximus (GM) is relaxed and unable to tension the lumbosacral fascia. This means the Errector Spinae (ES) muscle group must therefore perform the entire lumber extension workload.
This article discusses the link between lower back pain and the following muscle problems:-
Shortening of the hamstring muscle.
Overworking of the Erector Spinae muscle group and the development of trigger points.
Overworking of the Iliopsoas muscle group and the development of trigger points.
Hamstrings are shortened and inactive while sitting causing tension. This is so common I will write a separate blog most on Hamstrings.
Without the help of the Gluteal muscles the Erector Spinae muscles become tired and painful very quickly and struggle to maintain the correct "hollow" in your lower back. Even thought you may consider sitting an apparently restful posture it is actually an intense workout for the Erector Spinae and the Iliopsoas muscle groups.
If you are not using a full and appropriately shaped chair back, your Iliopsoas muscles must pull your torso forward to stop you falling backward, and they have to do that at the short end of their range of contractile length. That is a sure fire recipe for Iliopsoas muscle shortening and development of trigger points. Here are some indications that you have a shortened Iliopsoas
Diffuse achy - type pain radiating out from the groin area to the lower back, and possibly around to the side of the hip and the butt area. If the trigger points in the groin are not pressed, the pain is not sharp or stabbing.
Relief of pain is often experienced by sitting down.
Worse upon lengthening the iliopsoas, i.e. when one stands up, or straightens the hip joint.
Worse for doing situps.
Worsened by externally rotating the hip (i.e. making the knee cap look outward) when the hip joint is fully extended.
In patients with sciatic nerve pain, lying flat on one's back with the legs out straight causes the trigger point tightened iliopsoas to compress the lumbar vertebrae together, with the result that the nerve roots of the sciatic nerve are compressed too.
When lying flat on one's back, doing a straight leg raise reveals weakness on the affected side.
In patients with sciatic nerve pain due to nerve root compression, lying flat on one's back with legs out straight stretches that trigger point tightened iliopsoas. The result is that the iliopsoas compresses the lumbar vertebrae together, and the the nerve roots of the sciatic nerve are compressed at the same time.
All the side effects of sitting for long periods of time can be addressed by deep tissue massage.